A conservative zero-till cropping strategy with added manure and high nitrogen applications has proven to be the best-performing system to maximise returns in Central Queensland.

Long-term farming systems research, led by Darren Aisthorpe from the Queensland Department of Agriculture and Fisheries (DAF), has tested 10 systems – from a conservative approach to a higher fertility one – for nearly 10 years.

The standout system has been ‘higher fertility’. It uses a conservative zero-till approach and targets one crop each year: wheat, barley, chickpeas or sorghum.

Its nitrogen and phosphorus rates target the 90th percentile of yield potential based on soil moisture in a variable environment.

An additional 60 tonnes per hectare of feedlot manure (wet weight) was applied to lift the starting soil fertility level. One application (20 t/ha) was made in early 2015, and the second (40 t/ha) in late 2016.

Mr Aisthorpe says the system was never designed to be a ‘manure’ system. “The intention was to raise the fertility of the soil to what it might have been when cropping first started. That way, we could see if higher initial soil fertility could be maintained with higher nutrient inputs based on the 90th percentile.”

Using manure to lift soil organic matter was also expected to slowly release more nitrogen from mineralisation like a ‘younger’ soil does and provide a more even distribution of nitrogen down the profile for better crop growth.

“We know that nitrogen further down the profile can be far more effectively taken up by the crop. Also, nitrogen fertiliser applied at planting is often poorly used by the crop, with perhaps only 20 per cent crop uptake that year.”

Top-tier differences

The ‘higher fertility or manure system’was not the only one tested that targeted the 90th percentile crop yield – the ‘higher nutrient supply system’ did too. The difference, however, was the additional manure.

“The ambition was that if additional water became available during the season, these systems would not lack available nitrogen or phosphorus, based on the modelled 90th percentile yields in APSIM (the Agricultural Production Systems SIMulator).”

Mr Aisthorpe says minimal additional nitrogen was needed for most of the trial, partly because of the site’s inherent high soil fertility. This led to negligible variation between the ‘baseline system’ (or common practice system) and the ‘higher nutrient supply system’.

Department of Agriculture and Fisheries team members Jane Auer and Katie Hullock (in the ute) took soil cores for water and nutrition levels in mid-December 2023 at the Emerald site. Photo: Supplied by Darren Aisthorpe

In comparison, the ‘higher fertility or manure system’ was “an excellent example of what can happen when a system is mined. No nitrogen was applied to that system after 2016 and its performance was (and still is) stellar”.

Mr Aisthorpe says this system also stood out because of “how poorly the ‘just-in-time’ nutrition strategy performed. Even with the 90th percentile nutrient strategy in place, it failed to maintain its fertility levels during a high production period post-2021”.

Between August 2021 and September 2023, the system grew one cover crop (millet) followed by three grain crops (grain sorghum, chickpeas and wheat). It created 34.8 tonnes per hectare of biomass or 13.2t/ha of grain.

During this time, available nitrogen in the profile dropped from more than 500 kilograms/ha to 114kg/ha in the top 90 centimetres, with more than 90kg/ha of that total sitting below 60cm.

However, all was not completely lost to the system. “You only need to look at how little net nitrogen was removed after the 2022 sorghum crop across the systems, relative to the crop yields and biomass produced, to understand that nitrogen tied up in the millet residue had already started returning to the system,” Mr Aisthorpe says.

“That residue broke down quickly after desiccation in early November 2021, and by chickpea planting in 2022, ground cover was limited.

“It will be interesting to track this system moving forward. Even if the organic carbon boost from the manure has been used, the additional benefits of significant amounts of phosphorus, potassium and other nutrients in the manure will still be present and may continue to offer an advantage for some time yet.”

Magic manure

So, should growers be sourcing manure? Mr Aisthorpe says there is no doubt that the higher-fertility system is the best-performing one in terms of gross margin based on a simulated scenario using nine years of data for a 2000ha cropping enterprise with 560 millimetres of annual rainfall.

“However, our economics do not include application of manure costs. The application price at our rates could be $2200/ha to replicate if the transport from a feedlot to the farm is 100km.”

Table 1: Case study showing what value per mm each system would have provided annually for a 2000ha enterprise with an annual rainfall of 560mm. Enterprise $/mm of rainfall shows the system value per mm to the entire enterprise. Enterprise Annual $GM extrapolates out the gross margin per ha across a commercial enterprise
of 2000ha.

Source: DAF

Table 1 demonstrates a case study, showing what value (gross margin) per millimetre of rainfall each system would have provided annually (average over nine years) for a 2000ha enterprise, with an annual rainfall of 560mm.

Enterprise $/mm of rainfall shows the system value per millimetre to the entire enterprise. Enterprise Annual $GM extrapolates the gross margin per hectare.

The annual difference in gross margin between the best – the ‘higher fertility (manure) system’ and the lowest - ‘higher crop intensity’ was $948,000 per year.

“Even the gap between the ‘higher fertility (manure) system’and the ‘baseline system’ was $330,000 per year, which is still significant.”

However, Mr Aisthorpe says these numbers do not necessarily tell the entire story.

“If you could get sufficient manure, the cost would reduce its ranking below the ‘higher legume system’ to about $1.29/ha over the nine years.

“Equally, the ‘Integrated Weed Management (IWM) system’ and the ‘higher legume systems’ had outperformed ‘baseline’ consistently until recently, but at what cost to soil fertility?

“Even the ‘higher nutrient supply’ and ‘higher fertility’ systems may have looked quite different if the higher nutrient calculations had been a fixed value, versus a trigger level nutrition policy.

“Of the four split systems, ‘IWM + nutrition’ annual gross margin is certainly impressive and a possible indication of what ‘IWM’could have been. However, given how recent their introduction has been, I would still consider those values with scepticism.”

What the research does highlight is that systems matter, he says.

“For the Emerald site, a more conservative cropping strategy on a non-limiting nutrition plan has been the most consistent strategy to maximise returns.

“It sounds basic, but planting into plenty of moisture, at an optimal sowing date for that crop to reduce stress risk, with non-limiting nutrition, will always produce the best outcomes over the long term.

“Any system that has been ‘pushed’ because of plant-available water, sowing date, sowing depth, crop choice or density, has at some point in time taken a hit and rarely been able to catch up that lost ground.”

The research

The work is part of an extensive field-based farming systems research program with CSIRO and the NSW Department of Primary Industries.

System modifications are being tested across six locations at Emerald, Billa Billa, Mungindi, Spring Ridge, Narrabri and Trangie.

The core experimental site near Pampas on the eastern Darling Downs compares 34 different systems.

The Northern Farming Systems project concentrates on how farming systems’ modifications affect water use efficiency, nutrient balance and nutrient use efficiency, changes in pathogen and weed populations, changes in soil health, and profitability.

Queensland Department of Agriculture and Fisheries (DAF) senior research agronomist Darren Aisthorpe says the system modifications being tested are crop intensity, increased legume frequency, increased nutrient supply and increased crop diversity.

The initial six systems established are:

1. ‘Baseline’ – This conservative zero-tillage system targets one crop each year. Crops are limited to wheat, barley, chickpeas and sorghum, with nutrient application rates on cereals targeting median (or 50th percentile) seasonal yield potential. It is aligned with the ‘baseline’ system at the Pampas core site.
2. ‘Higher crop intensity’ – This focuses on increasing the cropping intensity to an average of 1.5 crops a year, when water allows. Crops include wheat, chickpeas, sorghum, mungbeans and forage crops or legumes. Nitrogen rates on cereals targeting median (50th percentile) seasonal yield potential. It is aligned with the ‘+intensitysystem’ at the Pampas core site.
3. ‘Higher legume’– The frequency of pulses in the ‘baselinesystem’ is increased (one pulse crop every two years) to assess the impact of more legumes on profitability, soil fertility, disease and weeds. Nitrogen rates on cereals targeting median (50th percentile) seasonal yield potential. This is aligned with the ‘+legumesystem’ at the Pampas core site.
4. ‘Higher nutrient supply’ – The nitrogen and phosphorus rates of the ‘baseline system’ are increased targeting the 90th percentile of yield potential, based on soil moisture in an environment of variable climate. The crops and other practices are the same as the ‘baselinesystem’. This is aligned with the ‘+nutrient system’ at the Pampas core site.
5. ‘Higher soil fertility’– This is based on the ‘higher nutrient supply’system, with an additional 60 tonnes per hectare of manure (wet weight) applied to change the starting soil fertility level. This system is designed to see whether higher initial soil fertility can be maintained with greater nutrient inputs (90th percentile). It is aligned with the ‘+fertilitysystem’ at the Pampas core site.
6. ‘Integrated weed management’(IWM) (X01) – This minimum-tillage system is focused on one crop a year but employs practices to reduce the reliance on traditional knockdown herbicides. Crops include wheat, chickpeas, sorghum and mungbeans with nitrogen rates on cereals targeting median (50th percentile) seasonal yield potential.

Mr Aisthorpe says these six systems were maintained until after the winter crop of 2020. The project was then extended, and four additional systems were added.

These include:

1. ‘Baseline + higher diversity’– How does a moderate intensity (‘baseline’) system using a diverse crop selection compare with the other systems?
2. ‘Higher legume + nutrition’ – Higher legume system + pre-crop nutrition calculations are now performed to target a 90th percentile yield instead of a 50th percentile. With nitrogen stratification at sowing a significant issue for Central Queensland, it is expected that fertiliser might be for the following crop, not the current crop.
3. ‘Lower intensity + nutrition’ – How does a low-intensity, high-nutrition system using a diverse crop selection compare against the other systems?
4. ‘IWM + nutrition’ – Standard IWM system plus pre-crop nutrition calculations are now performed to target the 90th percentile. The standard IWM system demonstrated a consistent decline in baseline fertility relevant to other systems. By increasing nutrition levels, improved production and system benefits could occur.

More information: Darren Aisthorpe, darren.aisthorpe@daf.qld.gov.au